bed_mesh_fast: Disable on RELATIVE_REFERENCE_INDEX

README.md

@@ -26,8 +26,8 @@ with g-code targeting Marlin printers. However, there are also some nice extras:
   provided a much easier way to customize materials in the LCD menu (or at least
   I think so). I've also added confirmation dialogs for commands that would
   abort an active print.
-* **[Optimized mesh bed leveling](#bed-mesh-improvements)** - Probes only within the
-  printed area, which can save a lot of time on smaller prints.
+* **[Optimized mesh bed leveling](#bed-mesh-improvements)** - Probes only within
+  the printed area, which can save a lot of time on smaller prints.
 
 ## A few warnings...
 
@@ -267,6 +267,11 @@ The following additional configuration options are available from
 
 > **Note:** See the [optional section](#bed-mesh) for additional macros.
 
+> **Note:** The bed mesh optimizations are silently disabled for delta printers
+  (because jinja2 lacks the necessary math support) and when the mesh parameters
+  include a [`RELATIVE_REFERENCE_INDEX`](https://www.klipper3d.org/Bed_Mesh.html#the-relative-reference-index)
+  (which is cinompatible with dynamic mesh generation).
+
 `BED_MESH_CHECK`
 
 Checks the `[bed_mesh]` config and warns if `mesh_min` or `mesh_max` could allow

bed_mesh_fast.cfg

@@ -8,8 +8,12 @@ gcode:
   {% set probe_count_scale = km.probe_count_scale %}
   {% set bed_mesh = printer.configfile.config.bed_mesh %}
 
-  # Don't have the math functions available to work on a delta bed.
-  {%if "mesh_radius" not in bed_mesh %}
+  # Don't have the math functions available to work on a delta bed, and
+  # not sure how to make relative reference index work.
+  {%if "mesh_radius" not in bed_mesh and
+       "MESH_RADIUS" not in params and
+       "relative_reference_index" not in bed_mesh and
+       "RELATIVE_REFERENCE_INDEX" not in params %}
     {% set safe_min_x = bed_mesh.mesh_min.split(",")[0]|float %}
     {% set safe_min_y = bed_mesh.mesh_min.split(",")[1]|float %}
     {% set safe_max_x = bed_mesh.mesh_max.split(",")[0]|float %}